We wish to determine the structural and functional significance of histones and of relatively abundant nonhistone proteins in the eukaryote chromosome, and of histone-like proteins in the prokaryote chromosome. The work consists of three different but mutually interdependent lines of research, namely: 1) Detailed structural analysis of sub-, mono- and oligonucleosomes in mild nuclease digests of chromatins from human, mouse and Drosophila cell lines using in particular, new electrophoretic techniques for separation and analysis of deoxyribonucleoprotein (DNP) particles recently developed by us. 2) Studies on the structure of the prokaryotic (Escherichia coli) chromosome, in particular, studies on interactions between two specific histone-like proteins recently found by us in the highly purified E. coli DNP. In addition, a search for a possible nucleosome-like organization of the E. coli chromosome will be carried out, using various nucleases as probes. 3) Studies on the structure of the SV 40 viral minichromosome as a model of the cellular chromatin structure. In particular, we shall use the minichromosome to investigate the problem of the relationship between nucleosomes and base sequences in DNA and study DNA folding in the minichromosome using new experimental approaches and the recently described compact form of the SV40 minichromosome as a starting material.